This invention relates to a vehicle lamp in which the joining portion of a lamp body, which is used to form a vehicle lamp such as a vehicle sign lamp, is directly welded to the joining portion of a lens adapted to cover the opening of the lamp body, and more particularly to a vehicle lamp and its vibration type welding method in which the joining portions of the two components are partially molten by the frictional heat which is generated by electromagnetic vibration, and are then cooled so as to be welded together.
A vehicle lamp is available which is formed by directly welding a joining portion of a lamp body of thermoplastic synthetic resin to a front lens of thermo-plastic synthetic resin. That is, a vehicle lamp is available which is formed by a so-called "hot-plate type welding method". The vehicle lamp 51 formed according to the method is generally shown in FIG. 11. As is seen from FIG. 11, the vehicle lamp 51 is advantageous in that the welding portion 54 of the lamp body 52 and the front lens 53 where those components are welded together is small in thickness, and therefore its effective area is large enough in the limited space of the vehicle body. The hot-plate type welding method is practiced as follows: A metal plate at a high temperature held between the welding portions 54 of workpieces, namely, the lamp body 52 and the front lens 53 which are to be welded together. That is, the welding portions of the workpieces, namely, the leg 52a of the lamp body 52 and the leg 53a of the front lens 53 are thermally deformed or thermally molten by heating the metal plate, so that they are welded together to form the vehicle lamp.
However, the vehicle lamp 51 formed by the hot-plate type welding method is disadvantageous in the following points: As shown in FIG. 12, bubbles c, c, . . . are liable to be formed in the weld 54 which is formed by welding the leg 52a of the lamp body 52 and the leg 53a of the front lens together. Furthermore, since the weld 54 is relatively large, which impairs the external appearance of the vehicle lamp. In addition, the weld is formed by welding the ends of the legs 52a and 53a of the lamp body 52 and the front lens 53, and therefore the weld 54 is not only low in welding strength but also brittle. In the manufacture of the vehicle lamp, the heated metal plate is used, which increases the ambient temperature, thus worsening the environmental working condition and adversely affecting the performance of the peripheral equipment.
The vehicle lamp formed according to the hot-plate type welding method suffers from the following difficulty: As is seen from FIG. 11, when the vehicle is traveling in a rainy day, water drops striking the front lens 53 may flow over the side wall of the lamp body 52 to the back of the latter to enter the lamp chamber through ventilating pipes, or wets the electrical system of the vehicle lamp, resulting in the occurrence of a trouble therewith.